JP2004062976A - Optical disk, optical disk reproducing device, and optical disk reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk capable of raising the amount of reflected light from reflective layers of the multilayers in an optical disk having multilayered structure having reflective layers of two or more layers. <P>SOLUTION: The optical disk having the multilayered structure provided with a first reflective layer 12 having reflecting and transmitting functions of light and a second reflective layer 15 having only the reflecting function of light is provided with a transparent dielectric layer 13 which is arranged to be adjacent to the first reflective layer 12 and which gives multiplex interference effect to a light beam irradiating the layer 13. <P>COPYRIGHT: (C)2004,JPO

Description

【００４８】
上記表１に示した結果では、透明誘電体層１３を設けない場合を従来例とし、該従来例の光ディスクにおける第１反射層からの反射光量（第１層反射光量）および第２反射層からの反射光量（第２層反射光量）をそれぞれ１００とした。
【００４９】
透明誘電体層１３を設けた例では、該透明誘電体層１３の屈折率を１．６，１．８、２．２の３種類とし、第１反射層１２にフォーカスをロックした時の反射光量を従来例の第１層反射光量で割ったパーセント比率を第１反射層１２における反射光量比として示した。同様に、第２反射層１５にフォーカスをロックした時の反射光量を従来例の第２層反射光量で割ったパーセント比率を第２反射層１５における反射光量比として示した。
【００５０】
透明誘電体層１３の屈折率を１．６とした例では、該透明誘電体層１３の膜厚を３０，６０，１００ｎｍとした３種類の光ディスク１０を作製し、うち膜厚６０ｎｍのものを実施例１とした。また、透明誘電体層１３の屈折率を１．８とした例では、該透明誘電体層１３の膜厚を１０，２０，３０，４０，６０ｎｍとした５種類の光ディスク１０を作製し、うち膜厚４０ｎｍのものを実施例２とした。また、透明誘電体層１３の屈折率を２．２とした例では、該透明誘電体層１３の膜厚を１０，２０，３０，４０，６０ｎｍとした５種類の光ディスク１０を作製し、うち膜厚３０ｎｍのものを実施例３、膜厚６０ｎｍのものを比較例１とした。
【００５１】
すなわち、上記表１に示した結果において、透明誘電体層１３の屈折率を１．６，１．８，２．２に設定したそれぞれの光ディスク１０において、第２層反射光量比が最も大きくなる膜厚の場合を実施例１ないし３としている。また、透明誘電体層１３の屈折率を２．２に設定した光ディスク１０において、第２層反射光量比に変化がない膜厚の場合を比較例１としている。
【００５２】
尚、上記表１における結果は、光ディスクのミラー部での反射光量を比較した結果によるものである。但し、光ディスクに記録される情報に対応した凹凸が存在する領域の再生信号についても上記と同様の実験によって確認し、信号の最大値が得られる条件がミラー部の反射光量が最大となる条件と一致していることを確認している。すなわち、上記表１の結果、およびこれに基づく以下の考察は、実際の再生信号光量を反映していると考えてよい。
【００５３】
上記表１の結果を第１層・第２層反射光量比についてそれぞれグラフ化したものが図３および図４である。尚、図３および図４では、横軸に透明誘電体層１３の膜厚、縦軸に第１層反射光量比（または第２層反射光量比）を示しているが、横軸に記載の膜厚範囲を０〜６０ｎｍとしている。
【００５４】
上記図３および図４の結果より、透明誘電体層１３を設けることによって、従来例に比べ、第１反射層１２および第２反射層１５のそれぞれにおける反射光量が向上し、光利用効率が向上することが分かった。
【００５５】
すなわち、第１反射層１２に光線のフォーカスをロックして照射を行う際には、透明誘電体層１３内において多重反射が発生し、これらの多重反射光が互いに強めあう方向に多重干渉する時、第１反射層１２からの反射光強度が向上する（第１反射層１２の反射率が増加する）。
【００５６】
また、第２反射層１５に光線のフォーカスをロックして照射を行う際には、第２反射層１５に照射される光線は透明誘電体層１３を透過する。しかしながら、この際にも、透明誘電体層１３において幾分かの多重反射は発生し、これらの多重反射光が互いに強めあう方向に多重干渉する時、第２反射層１５からの反射光強度が向上する。但し、透明誘電体層１３での多重干渉による反射光強度向上の効果は、第１反射層１２からの反射光強度の向上効果に比べ、第２反射層１５からの反射光強度の向上効果の方が小さい。本実施の形態に係る光ディスク１０の固定条件、特に第１反射層を金１５ｎｍとした場合、透明誘電体層１３の屈折率が大きいと第１層反射光量比に特に著しい光利用効率向上の効果が得られる。
【００５７】
また、透明誘電体層１３の屈折率については、屈折率が大きい方が第１層反射光量比および第２層反射光量比ともにその最大値が大きくなる。すなわち、実施例１＜実施例２＜実施例３の順で光利用効率向上の効果が見られた。また、屈折率が大きいほど第１層反射光量比および第２層反射光量比の最大値を取る膜厚が小さくなる。
【００５８】
第１層反射光量比および第２層反射光量比はともに、透明誘電体層１３がある程度の膜厚となる時に極大値を示し、透明誘電体層１３の膜厚が大きくなりすぎるとピークを取った後減少に転じる。尚、第１反射層１２および第２反射層１５の材質等によっては、第１層反射光量比および第２層反射光量比のそれぞれが極大値を取るための透明誘電体層１３の膜厚が一致しない場合もある。その場合には、トータルで考慮し、両光量比がともに向上する望ましい条件を選択すればよい。
【００５９】
以上の実験結果に基づき、本発明の光ディスク１０において以下の好適な実施形態が導かれる。
【００６０】
先ず、上述の結果より、透明誘電体層１３の屈折率ｎは、ｎ＞１．６において、光利用効率が向上しており、さらに、透明誘電体層１３の屈折率が大きいほど、より光利用効率が向上している。
【００６１】
これは、透明誘電体層１３と第２母材１４との境界面において反射を生じさせるためには、透明誘電体層１３と第２母材１４とが屈折率に差を持つことが必要なためであり、かつ、その差が大きいほど多重反射が多くなる（多重干渉の効果が大きくなる）。
【００６２】
そして、透明誘電体層１３と第２母材１４との屈折率の大小は、透明誘電体層１３の屈折率の方が小さい場合であっても原理的には多重干渉による反射光強度の向上効果は得られるものの、第２母材１４の屈折率は通常１．５程度であり、透明誘電体層１３の屈折率の方が小さい場合には透明誘電体層１３と第２母材１４とが屈折率の差を大きくとることは難しい。
【００６３】
このため、透明誘電体層１３は第２母材１４よりも屈折率の大きい材質を選択することが好ましい。また、透明誘電体層１３の光路長は（透明誘電体層１３の屈折率ｎ）×（透明誘電体層１３の膜厚ｄ）で決まるので、少ない膜厚ｄで同じ効果を得るためにも透明誘電体層１３の屈折率ｎは大きいほうが望ましい。
【００６４】
また、上記図３および図４では、第１層反射光量比および第２層反射光量比は、透明誘電体層１３の膜厚がある程度の値となるとき極大値となり、その後は透明誘電体層１３の膜厚が大きくなるにつれて減少している。しかしながら、本発明は光の多重干渉を利用した光利用効率向上技術であるため、実際には、図５に示すように、第１層反射光量比および第２層反射光量比は、透明誘電体層１３の膜厚に対してある一定の周期にて増減を繰り返し、透明誘電体層１３の膜厚がλ／２ｎ増加する毎に極大値が発生する。図５は透明誘電体層１３の膜厚と、第１反射層１２および第２反射層１５の反射率との関係をシミュレーションによって計算し、その結果をグラフ化したものである。
【００６５】
尚、図５のグラフは、各層の屈折率と膜厚とを各パラメータとして仮定し、仮想の多層膜での光学計算によって求められている。これに比べ、図３および図４は、膜厚０すなわち透明誘電体層を設けない場合の反射率を１００％として規格化したものであり、図５とは絶対値が異なっている。
【００６６】
また、第１層反射光量比および第２層反射光量比における最初の極大値は、透明誘電体層１３の光路長（ｎｄ）が、光ディスク１０に照射される光線の波長の１／２よりも小さくなる期間で必ず発生する。すなわち、透明誘電体層１３の膜厚ｄが０＜ｎｄ＜λ／２を満たす中で、該透明誘電体層１３の膜厚を設定し、光利用効率を向上させることができる。但し、本発明の技術思想は上記条件に限るものではなく、膜厚がさらに大きい場合（すなわち、２回目以降の極大値が生じる膜厚となる場合）の多重干渉を利用した光利用効率向上をも含むものである。
【００６７】
また、透明誘電体層１３は、第２層反射光量比よりも第１層反射光量比に対して、特に著しい光利用効率向上の効果を与えるものである。すなわち、従来例よりも第１反射層１２の反射光量が特に増強されるので、第２反射層１５を再生する場合には、第２反射層１５の反射光に第１反射層１２の反射光がノイズとして悪影響を与える可能性がある。但し、前述のように、第１反射層１２を主要な記録領域として利用し、第２反射層１５を補助の記録領域として利用する場合には、第１反射層１２だけでも良好に走査できることは有用である。
【００６８】
但し、第２反射層１５の反射光におけるノイズをできるだけ小さくするためには、透明誘電体層１３の膜厚を第２層反射光量比の極大値を与える膜厚に設定するとよい。例えば、透明誘電体層１３の屈折率が２．２の場合において、実施例３と比較例１とを比べると、第１層反射光量比については比較例１の場合の方が大きいが、第２層反射光量比が最大となる実施例３の方が第１層反射光量比と第２層反射光量比との差が小さく、第２反射層１５の反射光に対する第１反射層１２の反射光によるノイズを小さくできる。
【００６９】
さらに、第１反射層１２の反射光量と第２反射層１５の反射光量とのバランスを保ちたい場合には、第１反射層１２の膜厚調整を含めたさらなる光利用効率の最適化が可能となる。
【００７０】
すなわち、第１反射層１２の反射光量は、透明誘電体層１３での多重干渉によって大幅に向上させることが可能であり、第１反射層１２の膜厚を１５ｎｍよりもさらに薄くして第１反射層１２の透過率を大きくしても、従来例より大きな反射光量を得ることが可能である。一方、第２反射層１５の反射光量は透明誘電体層１３での多重干渉による向上は少ないものの、第１反射層１２の膜厚を薄くして第２反射層１５の反射光量に振り分けることで直接的に向上させることができる。
【００７１】
これにより、第１反射層１２の反射光量と第２反射層１５の反射光量とがほぼ同じとなるように最適化することも可能である。尚、この時、薄膜化により第１反射層１２は透過率が変わるのみで屈折率の値には変化がないため、透明誘電体層１３での多重干渉効果も変化せず、上述の考察における屈折率・膜厚条件はそのまま転用できるものである。
【００７２】
また、上述のように第１反射層１２に光線のフォーカスを確実にロックできれば、この位置を基準として光線のフォーカスを第２反射層１５に移動させることは容易なので、第１および第２反射層１２・１５の両方にフォーカスを良好にロックさせることができる。
【００７３】
また、透明誘電体層１３の膜厚は光の多重干渉を利用するための層であるため、数１０〜数１００ｎｍのオーダーであり、これは第１反射層１２成膜後に引き続きスパッタリングなどの薄膜技術により形成することができるので生産性も良好である。
【００７４】
透明誘電体層１３以外の各層は従来の光ディスクと同様の構成であるので、スピンコートやスパッタリングなどの薄膜技術により形成することができ、生産性も良好である。
【００７５】
尚、以上の説明における光ディスク１０は、第１母材１１が一般的に呼称される基板と同一であり基板側から光が入射する構成として示した。しかしながら、近年、高密度化を目的として基板を通さず膜面側から光入射する方式が提案されており、本発明は膜面側からの光入射の再生方式においても適用可能である。但しその場合は媒体構成が逆になるため、図６に示すように、光ディスク１０’において、第１母材１１、第２反射層１５’、第２母材１４、透明誘電体層１３’、第１反射層１２’、保護層１６という順序になり、光は保護層１６側から入射される。また、上記構成の光ディスク１０’において、媒体構成は異なっても光学的な光路や多重干渉による光利用効率向上の原理は上記で説明した光ディスク１０の場合と同様であり、光の入射方向に応じて構成を変化させれば本発明を適応することができる。
【００７６】
また、本実施の形態では２層構成の媒体について説明したが、媒体構成としては２層に限定するものではなく、透明誘電体層を本実施の形態と同様に、反射／透過の機能を有する反射層に隣接させ、かつ光入射側の反対側に設けることにより、本発明を３層構成、４層構成などのより多層の構造にも応用することができる。
【００７７】
このように、本実施の形態に係る光ディスク１０では、第１反射層１２および第２反射層１５からの反射光強度を透明誘電体層１３の多重干渉効果によって向上させることができるものであり、該光ディスク１０を再生する再生装置および再生方法では、従来の再生に比べて照射する光線の出力を下げても良好な再生信号を得ることができる。このため、上記光ディスク１０を再生する光線が、これに適した出力に設定されている場合、従来に比べ低消費電力を達成することができる。
【００７８】
また、光線の出力が特に上記光ディスク１０に合わせた設定となっていない従来の光ディスク再生装置においても、該光ディスク１０の再生を行うことは可能であり、この場合は、第１反射層１２および第２反射層１５からの反射光強度が向上することで、より良好な再生信号が得られる。
【００７９】
【発明の効果】
本発明の光ディスクは、以上のように、上記第１反射層と隣接して配置され、情報再生のために照射される光線に対して多重干渉効果を与える透明誘電体層を備えていることを特徴としている。
【００８０】
それゆえ、上記第１反射層に光線のフォーカスをロックして照射を行う際には、透明誘電体層内において多重反射が発生し、これらの多重反射光が互いに強めあう方向に多重干渉することで、第１反射層からの反射光強度が向上する。また、第２反射層に光線のフォーカスをロックして照射を行う際には、第２反射層に照射される光線が透明誘電体層を透過する際に、透明誘電体層において多重反射が発生し、これらの多重反射光が互いに強めあう方向に多重干渉することで、第２反射層からの反射光強度が向上する。
【００８１】
これにより、２層以上の反射層を有する多層構造の光ディスクにおいて、これら多層の反射層からの反射光量を向上させることができるといった効果を奏する。
【００８２】
また、上記光ディスクにおいて、上記透明誘電体層は、第１反射層に対して上記光線の入射側の反対側に設けられる構成とすることが好ましい。
【００８３】
それゆえ、上記透明誘電体層における多重干渉の効果が顕著となるといった効果を奏する。
【００８４】
また、上記光ディスクにおいて、上記透明誘電体層の屈折率は、上記光線の入射側の反対側で接する母材の屈折率よりも大きい値を有することが好ましい。
【００８５】
それゆえ、上記透明誘電体層の屈折率と上記母材の屈折率との差を大きくすることが容易となり、多重干渉効果を大きくすることができるといった効果を奏する。また、上記透明誘電体層の膜厚を小さくして多重干渉効果を得ることができるといった効果を奏する。
【００８６】
また、上記光ディスクにおいて、上記透明誘電体層の膜厚は、該透明誘電体層の屈折率をｎ、膜厚をｄ、上記光線の波長をλとする時、０＜ｎｄ＜λ／２を満たす範囲で設定されることが好ましい。
【００８７】
それゆえ、透明誘電体層の膜厚が０＜ｎｄ＜λ／２を満たす中で該透明誘電体層の膜厚を設定することで、透明誘電体層の膜厚を最小として上記多重干渉効果を得ることができ、光利用効率を向上させることができるといった効果を奏する。
【００８８】
また、上記光ディスクにおいて、上記透明誘電体層は、ＡｌＮ、ＳｉＮ、ＡｌＳｉＮ、ＡｌＴａＮ、ＴａＯ、ＳｉＯ、ＳｉＯ_２、ＴｉＯ_２、ＺｎＳ、Ａｌ_２Ｏ_３、ＳｉＡｌＯＨ、ＭｇＦ_２のうちの何れかの化合物からなる構成とすることが好ましい。
【００８９】
それゆえ、上記透明誘電体層を従来の作製手法を応用して作製することができるといった効果を奏する。
【００９０】
また、本発明の光ディスク装置は、以上のように、光ディスクを再生するための光線を出射する光源の出力が、上記構成の光ディスクを再生するのに適した出力に設定されていることを特徴としている。
【００９１】
また、本発明の光ディスク方法は、以上のように、光ディスクを再生するための光線の出力が、上記構成の光ディスクを再生するのに適した出力にて照射されることを特徴としている。
【００９２】
本発明に係る光ディスクでは、第１反射層および第２反射層からの反射光強度を透明誘電体層の多重干渉効果によって向上させることができる。このため、上記光ディスクを再生する光ディスク再生装置および光ディスク再生方法では、従来の再生に比べて照射する光線の出力を、上記光ディスクを再生するのに適した出力に設定することで、従来の再生に比べ低消費電力を達成することができるといった効果を奏する。
【図面の簡単な説明】
【図１】本発明の一実施形態を示す２層構造の光ディスクの断面図である。
【図２】上記光ディスクの再生を行う光ディスク再生装置の概略構成を示す図である。
【図３】上記光ディスクにおける透明誘電体層の膜厚と第１層反射光量比との関係を示すグラフである。
【図４】上記光ディスクにおける透明誘電体層の膜厚と第２層反射光量比との関係を示すグラフである。
【図５】上記光ディスクにおける透明誘電体層の膜厚と第１反射層および第２反射層の反射率との関係をシミュレーション結果にて示したグラフである。
【図６】本発明の他の実施形態を示す２層構造の光ディスクの断面図である。
【図７】従来の２層構造の光ディスクの断面図である。
【符号の説明】
１０，１０’　　光ディスク
１２，１２’　　第１反射層
１３，１３’　　透明誘電体層
１４　　　　　　第２母材（透明誘電体層と接する母材）
１５，１５’　　第２反射層
２１　　　　　　レーザー光源（光源）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical disk having a multilayer structure, an optical disk reproducing apparatus for reproducing the optical disk, and an optical disk reproducing method.
[0002]
[Prior art]
At present, an optical disk in which information is reproduced by a light beam is realized as a CD (Compact Disk), and an optical disk in which information is recorded by a light beam is realized as an MO (Magnet Optical Disk). Such an optical disc is intended to realize a large capacity and a high density of recorded information. In order to achieve a further large capacity and a high density, it has been proposed that the optical disc has a multilayer structure. A DVD (Digital Versatile Disk) has already been realized with two layers.
[0003]
An example of the structure of a conventional two-layer optical disc will be described below with reference to FIG. Here, the description will be made on the assumption that the light beam for reproducing the information is irradiated from the bottom to the top in the figure.
[0004]
In this optical disc 100, a first base material 101, a first reflective layer 102, a second base material 103, a second reflective layer 104, and a protective layer 105 are sequentially stacked from below, which is the incident direction of light rays, to above. Have been. The first base material 101, the second base material 103, and the protective layer 105 are made of a transparent resin. The first reflection layer 102 is made of a translucent metal film, and the second reflection layer 104 is made of a total reflection metal film.
[0005]
Irregularities corresponding to the recorded information are formed on the upper surfaces of the first and second base materials 101 and 103, and the first and second reflective layers 102 and 104 are formed according to the irregularities. That is, the information reproduced by the light beam is fixedly recorded by the unevenness of the first and second reflective layers 102 and 104.
[0006]
In the optical disc 100 having such a structure, information is fixedly recorded at the time of its production, like an existing CD, and this information is reproduced by a light beam. At this time, since the first reflective layer 102 and the second reflective layer 104 have different information recorded thereon, by adjusting the position of the focal point of the light beam emitted from below, the first and second reflective layers are adjusted. The information recorded on the layers 102 and 104 is individually reproduced.
[0007]
An example of a method for producing the optical disc 100 will be described below. First, a first base material 101 is manufactured by resin molding using a stamper (not shown) in which irregularities corresponding to information to be recorded on the first reflective layer 102 are formed in advance. A first reflective layer 102 is formed on the upper surface of the first base material 101 by sputtering metal.
[0008]
Next, a resin is poured into the surface of the first reflective layer 102, and a second base material 103 is formed by a stamper (not shown) for the second base material. The second reflective layer 104 is formed on the upper surface by sputtering metal. Finally, the optical disc 100 is produced by forming the protective layer 105 by resin molding.
[0009]
An optical disk reproducing device (not shown) for reading information from the first and second reflective layers 102 and 104 of the optical disk 100 is provided with a position of an objective lens 110 for condensing a light beam irradiated on the optical disk 100 on the reflective layer. Is adjusted to lock the focus on one of the first and second reflective layers 102 and 104. In the optical disc 100 as described above, it is generally considered that the first reflective layer 102 is mainly used and the second reflective layer 104 is used auxiliary.
[0010]
The above-described optical disc 100 functions in the same manner as an existing CD, but since information is recorded on each of the first and second reflective layers 102 and 104, the recording capacity of the information can be doubled.
[0011]
[Problems to be solved by the invention]
In the configuration of the conventional optical disc 100, the first reflective layer 102 needs to fulfill the following two roles.
{Circle around (1)} When the focus is locked on the first reflective layer 102, a role for reflecting light and reading only information recorded on the first reflective layer 102.
{Circle around (2)} When the focus is locked on the second reflection layer 104, a role for transmitting light and reading only information recorded on the second reflection layer 104.
[0012]
In order to satisfy the role of (1), the larger the reflectance of the surface of the first reflective layer 102 is, the larger the amount of reflected light including information of the first reflective layer 102 becomes, and the desired signal amplitude Is also advantageous. The properties of the first reflection layer 102 required at this time are that the film thickness is large, the reflectance is large, and the transmittance is small.
[0013]
On the other hand, in order to satisfy the role of the above (2), the first reflective layer 102 having a higher transmittance has a higher transmittance of light including information of the second reflective layer 104 (light reaching the second reflective layer 104). This is advantageous because the light amount increases and the target signal amplitude also increases. The properties of the first reflective layer 102 required at this time are that the film thickness is small, the reflectance is small, and the transmittance is large.
[0014]
As described above, the first reflective layer 102 is required to have different characteristics at the same time when focusing on the first reflective layer 102 and when focusing on the second reflective layer 104. Therefore, in practice, the light of the first reflection layer 102 is set so that both characteristics are satisfied, specifically, the signal light amounts of the first reflection layer 102 and the second reflection layer 104 are substantially the same. The transmittance has been adjusted. Alternatively, a slight light amount difference may be provided in order to distinguish between the first reflective layer 102 and the second reflective layer 104. However, if the signal light amount is too small, the noise becomes relatively large and the signal quality deteriorates. Therefore, in general, the light amount is adjusted to be substantially the same order.
[0015]
It is desirable that the light amount of the light beam incident on the optical disk 100 be low from the demand for lower power consumption in the optical disk reproducing device, and that the light amount be higher from the viewpoint of improving the signal quality. However, in the optical disc 100 having the above-described medium configuration, the first reflection layer 102 must simultaneously fulfill both of the above (1) and (2). There was room for improvement in terms of efficiency.
[0016]
The present invention has been made to solve the above problems, and an object of the present invention is to improve the amount of light reflected from these multilayer reflective layers in an optical disc having a multilayer structure having two or more reflective layers. It is to provide an optical disk that can be used.
[0017]
[Means for Solving the Problems]
In order to solve the above problems, the optical disc of the present invention includes at least one first reflection layer having a light reflection and transmission function, and one second reflection layer having only a light reflection function. The optical disc having a multi-layer structure is characterized in that the optical disc has a transparent dielectric layer disposed adjacent to the first reflective layer and providing a multiple interference effect to a light beam irradiated for information reproduction.
[0018]
According to the above configuration, when irradiation is performed with the focus of the light beam locked on the first reflection layer, multiple reflection occurs in the transparent dielectric layer, and the multiple reflection light is directed in a direction in which the multiple reflection light reinforces each other. Due to multiple interference, the intensity of light reflected from the first reflective layer is improved (the reflectivity of the first reflective layer is increased).
[0019]
Further, when the irradiation is performed while the focus of the light beam is locked on the second reflection layer, the light beam irradiated on the second reflection layer passes through the transparent dielectric layer. At this time, multiple reflections also occur in the transparent dielectric layer, and the multiple reflections of the multiple reflections interfere with each other in a direction that enhances each other, so that the intensity of the reflection light from the second reflection layer is improved. Reflectivity increases).
[0020]
Thus, in an optical disc having a multilayer structure having two or more reflective layers, the amount of light reflected from these multilayer reflective layers can be improved.
[0021]
Further, in the optical disc, it is preferable that the transparent dielectric layer is provided on a side opposite to the light incident side with respect to the first reflection layer.
[0022]
According to the above configuration, the multiple interference effect in the transparent dielectric layer is achieved by disposing the transparent dielectric layer adjacent to the first reflection layer on the side opposite to the light incident side. Becomes remarkable.
[0023]
Further, in the optical disc, it is preferable that a refractive index of the transparent dielectric layer has a value larger than a refractive index of a base material which is in contact with a side opposite to the light incident side.
[0024]
The greater the difference between the refractive index of the transparent dielectric layer and the refractive index of the base material, the greater the multiple interference effect. The refractive index of the base material is usually about 1.5, and by setting the refractive index of the transparent dielectric layer to be larger than the refractive index of the base material, the difference between these refractive indexes can be increased. It will be easier. In addition, the larger the refractive index of the transparent dielectric layer, the smaller the thickness of the transparent dielectric layer capable of obtaining the multiple interference effect.
[0025]
In the optical disk, the thickness of the transparent dielectric layer is defined as 0 <nd <λ / 2, where n is the refractive index of the transparent dielectric layer, d is the thickness of the transparent dielectric layer, and λ is the wavelength of the light beam. It is preferable to set within the range that satisfies.
[0026]
According to the above configuration, the amount of light reflected from the first reflective layer and the second reflective layer repeatedly increases and decreases with a constant period with respect to the thickness of the transparent dielectric layer. A maximum value occurs each time λ / 2n increases (because multiple interference of light is used). The first maximum value always occurs during a period in which the optical path length (nd) of the transparent dielectric layer is smaller than half the wavelength of the light beam irradiated on the optical disk. That is, by setting the thickness of the transparent dielectric layer while the thickness of the transparent dielectric layer satisfies 0 <nd <λ / 2, the thickness of the transparent dielectric layer is minimized and the light use efficiency is improved. Can be done.
[0027]
In the optical disc, the transparent dielectric layer is formed of AlN, SiN, AlSiN, AlTaN, TaO, SiO, SiO ₂ , TiO ₂ , ZnS, Al ₂ O ₃ , SiAlOH, MgF ₂ It is preferable to adopt a configuration consisting of any one of the above.
[0028]
According to the above configuration, as a material of the transparent dielectric layer, a material having a large transmittance and a high refractive index, and a material that is generally used is used, and the transparent dielectric layer is formed by applying a conventional manufacturing method. Can be manufactured.
[0029]
In order to solve the above-mentioned problems, the optical disc device of the present invention has at least one first reflection layer having a light reflection and transmission function and one second reflection layer having only a light reflection function. In an optical disc reproducing apparatus for reproducing an optical disc having a multilayer structure, the output of a light source for emitting a light beam for reproducing the optical disc is set to an output suitable for reproducing the optical disc having the above configuration. It is characterized by.
[0030]
According to another aspect of the present invention, there is provided an optical disc method comprising: at least one first reflection layer having a light reflection and transmission function; and one second reflection layer having only a light reflection function. An optical disk reproducing method for reproducing an optical disk having a multilayer structure, comprising: outputting an optical beam for reproducing the optical disk with an output suitable for reproducing the optical disk having the above configuration. .
[0031]
In the optical disk according to the present invention, the intensity of light reflected from the first reflective layer and the second reflective layer can be improved by the multiple interference effect of the transparent dielectric layer. In the reproducing method, a good reproduced signal can be obtained even if the output of the irradiated light beam is reduced as compared with the conventional reproducing method. Therefore, in the optical disk reproducing apparatus and the optical disk reproducing method set to the light beam output suitable for reproducing the optical disk, lower power consumption can be achieved as compared with the conventional reproduction.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
[0033]
The configuration of the optical disc according to the present embodiment will be described with reference to FIG. In the optical disk 10 shown in FIG. 1, the incident direction of the light beam is from the lower side to the upper side of the figure, and the optical disk 10 has a first base material 11, a first reflective layer 12, a transparent dielectric layer 13 , A second base material 14, a second reflective layer 15, and a protective layer 16 are sequentially stacked.
[0034]
The first and second reflection layers 12 and 15 are made of, for example, a metal having a high reflectance, and light is emitted from the optical disk 10 to be reflected by these reflection layers to reproduce information. The second reflection layer 15 is formed of a total reflection metal film, and generally, Al or an Al alloy is used. The first reflective layer 12 also needs to transmit light when reading the recorded information of the second reflective layer 15 in addition to the first reflective layer 12. Therefore, the first reflective layer 12 is formed of a thin film, and is generally made of gold, silver, Si, or the like. . However, as long as the metal has high reflectivity and satisfies the above conditions, the material of these reflective layers is not particularly limited to any metal.
[0035]
The transparent dielectric layer 13 is made of a material having a large transmittance and a large refractive index, and is a light reflected by the first reflection layer 12, a light transmitted to the second reflection layer 15, and a light reflected from the second reflection layer 15. Respectively cause an optical multiplex interference effect. Examples of materials that can be used for the transparent dielectric layer 13 include oxides and nitrides described below. That is, the transparent dielectric layer 13 is made of AlN, SiN, AlSiN, AlTaN, TaO, SiO, SiO ₂ , TiO ₂ , ZnS, Al ₂ O ₃ , SiAlOH, MgF ₂ And the like. Among them, AlN, SiN, AlSiN, AlTaN, TaO, SiO, SiO ₂ , TiO ₂ , MgF ₂ Is particularly desirable, but the material of the transparent dielectric layer 13 is not particularly limited as long as the above conditions are satisfied.
[0036]
The first base material 11, the second base material 14, and the protective layer 16 are made of, for example, a translucent organic resin. In the configuration according to the present embodiment, the first base material 11 is the same as a generally called substrate, and a typical material is a polycarbonate substrate or the like. A substrate made of such as can be used. Examples of the second base material 14 and the protective layer 16 include acrylic urethane UV curable resin, acrylic UV curable resin, polyurethane acrylate UV curable resin, and acrylic urethane UV curable resin. There is no particular limitation as long as conditions such as strength, residual stress, and durability are satisfied.
[0037]
Next, the specific layer configuration and manufacturing method of the optical disc 10 and the features of the present invention will be described.
[0038]
On a light-transmitting substrate made of polycarbonate having a thickness of 0.6 mm, in which projections and depressions corresponding to information to be recorded on the optical disk 10 are formed in advance, that is, on the first base material 11, gold is sputtered in an Ar atmosphere. Was formed to a thickness of 15 nm to form the first reflective layer 12. Continue Ar + N ₂ An AlN film was formed by reactive sputtering of an Al target in a mixed gas atmosphere to form a transparent dielectric layer 13. An ultraviolet-curable 2P resin was applied to the surface by spin coating to a thickness of 30 μm, and a stamper was pressed thereon and irradiated with ultraviolet rays to form a second base material 14. Further, Al was deposited to a thickness of 50 nm by sputtering in an Ar atmosphere to form a second reflective layer 15, a UV curable resin was applied thereon by spin coating, and then the protective layer 16 was cured by UV irradiation.
[0039]
The thickness of the second base material 14 is about 30 μm as in the conventional case, but the thickness of the transparent dielectric layer 13 is less than 1 μm because the transparent dielectric layer 13 is a layer for utilizing multiple interference of light. The second reflection layers 12 and 15 are separated from each other by about 30 μm as in the related art.
[0040]
Incidentally, in order to clarify the features and effects of the present invention, the optical disk 10 was manufactured by changing the refractive index and the film thickness of the transparent dielectric layer 13 and evaluated. N during reactive sputtering of AlN ₂ It is possible to change the composition ratio of AlN by changing the gas flow ratio, and since the refractive index changes according to the composition ratio of AlN, the refractive index of the transparent dielectric layer 13 is adjusted to a desired value by adjusting the sputtering conditions. Can be controlled. The thickness of the transparent dielectric layer 13 can be controlled by adjusting the sputtering time.
[0041]
With respect to the optical disk 10 thus manufactured, the focus was locked on each mirror portion (the area where no information is recorded) of the first and second reflective layers 12 and 15, and the amount of reflected light on each disk was compared.
[0042]
Here, FIG. 2 shows a schematic configuration of an optical disk reproducing apparatus used for reproducing the optical disk 10 according to the present embodiment. The optical disk reproducing device 20 shown in FIG. 2 includes a laser light source 21, a half mirror 22, an objective lens 23, a beam splitter 24, and photodiodes 25 and 26.
[0043]
At the time of reproducing the optical disk 10 by the optical disk reproducing device 20, the light beam emitted from the laser light source 21 is reflected by the half mirror 22, then is condensed by the objective lens 23, and the first reflective layer 12 or the second The light is applied to the reflection layer 15. The objective lens 23 is supported on the reflection optical path of the half mirror 22 so as to be movable in the optical axis direction. The optical disk 10 is supported at a position facing the objective lens 23 by a turntable (not shown).
[0044]
The reflected light reflected by the first reflection layer 12 or the second reflection layer 15 of the optical disc 10 is transmitted through the half mirror 22 and guided to a detection system for the reflected light. A beam splitter 24 is disposed in the transmission optical path of the half mirror 22, and two photodiodes 25 and 26 are disposed one by one in the spectral direction of the beam splitter 24. Here, it is assumed that the photodiode 25 is used for detecting a reproduction signal of recorded information, and the photodiode 26 is used for detecting a servo signal.
[0045]
In the present embodiment, it is assumed that the optical disk 10 and the optical disk reproducing device 20 are realized as mutually exclusive devices. In the following description, the optical disk Then, the information was reproduced by the optical disc reproducing apparatus 20 having the above configuration.
[0046]
Specifically, the optical disc 10 to be reproduced has the first base material 11, the second base material 14, and the protective layer 16 under the same conditions, the first reflective layer 12 has a thickness of 15 nm, and the second reflective layer 15 has After fixing the film thickness to 50 nm, the optical disc 10 is manufactured under various conditions with the refractive index of the transparent dielectric layer 13 in the range of 1.6 to 2.2 and the film thickness of 0 to 100 (nm). The amount of reflected light from the first reflective layer 12 and the second reflective layer 15 was evaluated. In the optical disk reproducing apparatus 20, the laser wavelength was 405 nm, the numerical aperture (NA) of the objective lens was 0.65, and the reproducing laser power was 1.5 mW. The evaluation results are shown in Table 1 below.
[0047]
[Table 1]

[0048]
In the results shown in Table 1, the case where the transparent dielectric layer 13 is not provided is taken as a conventional example, and the amount of light reflected from the first reflective layer (the amount of reflected light from the first layer) and the amount of light reflected from the second reflective layer in the conventional optical disc are considered. The amount of reflected light (the amount of reflected light in the second layer) was 100.
[0049]
In the example in which the transparent dielectric layer 13 is provided, the refractive index of the transparent dielectric layer 13 is set to 1.6, 1.8, and 2.2, and the reflection when the focus is locked on the first reflection layer 12 is determined. The percentage of the amount of light divided by the amount of reflected light of the first layer in the conventional example is shown as the ratio of the amount of reflected light in the first reflective layer 12. Similarly, the ratio of the amount of reflected light when the focus is locked to the second reflective layer 15 divided by the amount of reflected light in the second layer of the conventional example is shown as the ratio of the amount of reflected light in the second reflective layer 15.
[0050]
In the example in which the refractive index of the transparent dielectric layer 13 is 1.6, three types of optical disks 10 in which the thickness of the transparent dielectric layer 13 is 30, 60, and 100 nm are manufactured. Example 1 was used. In the example in which the refractive index of the transparent dielectric layer 13 is 1.8, five types of optical disks 10 in which the thickness of the transparent dielectric layer 13 is 10, 20, 30, 40, and 60 nm are manufactured. Example 2 having a film thickness of 40 nm was used. In the example in which the refractive index of the transparent dielectric layer 13 is 2.2, five types of optical disks 10 in which the thickness of the transparent dielectric layer 13 is 10, 20, 30, 40, and 60 nm are manufactured. A film having a thickness of 30 nm was referred to as Example 3, and a film having a thickness of 60 nm was referred to as Comparative Example 1.
[0051]
That is, in the results shown in Table 1 above, in each of the optical disks 10 in which the refractive index of the transparent dielectric layer 13 is set to 1.6, 1.8, and 2.2, the second layer reflected light amount ratio is the largest. Examples 1 to 3 are for the case of the film thickness. Further, in the optical disc 10 in which the refractive index of the transparent dielectric layer 13 is set to 2.2, the case where the film thickness does not change in the second layer reflected light amount ratio is taken as Comparative Example 1.
[0052]
The results in Table 1 are based on the results of comparing the amounts of light reflected by the mirror portion of the optical disk. However, the reproduction signal in the area where the unevenness corresponding to the information recorded on the optical disk is present is also confirmed by the same experiment as above, and the condition for obtaining the maximum value of the signal is the condition for maximizing the reflected light amount of the mirror section. Make sure they match. That is, the results in Table 1 above and the following considerations based on the results may be considered to reflect the actual amount of reproduced signal.
[0053]
FIG. 3 and FIG. 4 are graphs showing the results of the above Table 1 with respect to the first layer / second layer reflected light amount ratio, respectively. In FIGS. 3 and 4, the horizontal axis indicates the thickness of the transparent dielectric layer 13 and the vertical axis indicates the first layer reflected light amount ratio (or the second layer reflected light amount ratio). The thickness range is 0 to 60 nm.
[0054]
3 and 4, the provision of the transparent dielectric layer 13 improves the amount of reflected light in each of the first reflection layer 12 and the second reflection layer 15 as compared with the conventional example, and improves the light use efficiency. I found out.
[0055]
That is, when irradiating the first reflection layer 12 with the focus of the light beam locked, multiple reflection occurs in the transparent dielectric layer 13 and these multiple reflection lights interfere with each other in a direction that enhances each other. In addition, the intensity of light reflected from the first reflection layer 12 is improved (the reflectance of the first reflection layer 12 is increased).
[0056]
Further, when the irradiation is performed with the focus of the light beam locked on the second reflection layer 15, the light beam irradiated on the second reflection layer 15 passes through the transparent dielectric layer 13. However, also at this time, some multiple reflections occur in the transparent dielectric layer 13, and when these multiple reflections cause multiple interference in directions that enhance each other, the intensity of the reflection light from the second reflection layer 15 increases. improves. However, the effect of improving the intensity of the reflected light from the transparent dielectric layer 13 due to multiple interference is greater than the effect of improving the intensity of the reflected light from the first reflective layer 12. Is smaller. In the fixing condition of the optical disc 10 according to the present embodiment, particularly when the first reflective layer is made of gold of 15 nm, if the refractive index of the transparent dielectric layer 13 is large, the light use efficiency is particularly remarkably improved in the first layer reflected light ratio. Is obtained.
[0057]
Regarding the refractive index of the transparent dielectric layer 13, the larger the refractive index, the larger the maximum value of both the first layer reflected light amount ratio and the second layer reflected light ratio. That is, the effect of improving the light use efficiency was observed in the order of Example 1 <Example 2 <Example 3. In addition, the larger the refractive index, the smaller the film thickness at which the first layer reflected light amount ratio and the second layer reflected light amount ratio take the maximum value.
[0058]
Both the first layer reflected light amount ratio and the second layer reflected light ratio show a maximum value when the transparent dielectric layer 13 has a certain film thickness, and peak when the transparent dielectric layer 13 becomes too thick. Then turn to decrease. Depending on the material of the first reflection layer 12 and the second reflection layer 15, the thickness of the transparent dielectric layer 13 in which each of the first-layer reflection light quantity ratio and the second-layer reflection light quantity ratio takes a maximum value is determined. They may not match. In that case, it is sufficient to select a desirable condition that both the light quantity ratios are improved in consideration of the total.
[0059]
Based on the above experimental results, the following preferred embodiments are derived for the optical disc 10 of the present invention.
[0060]
First, from the above results, when the refractive index n of the transparent dielectric layer 13 is n> 1.6, the light use efficiency is improved, and the larger the refractive index of the transparent dielectric layer 13 is, the more light is emitted. Usage efficiency is improving.
[0061]
This means that in order to cause reflection at the interface between the transparent dielectric layer 13 and the second base material 14, it is necessary that the transparent dielectric layer 13 and the second base material 14 have a difference in refractive index. The greater the difference, the more the multiple reflections (the greater the effect of multiple interference).
[0062]
The magnitude of the refractive index between the transparent dielectric layer 13 and the second base material 14 is in principle improved even if the refractive index of the transparent dielectric layer 13 is smaller than that of the reflected light intensity due to multiple interference. Although the effect is obtained, the refractive index of the second base material 14 is usually about 1.5, and when the refractive index of the transparent dielectric layer 13 is smaller, the transparent dielectric layer 13 and the second base material 14 However, it is difficult to obtain a large difference in refractive index.
[0063]
For this reason, it is preferable to select a material having a higher refractive index than the second base material 14 for the transparent dielectric layer 13. Further, since the optical path length of the transparent dielectric layer 13 is determined by (refractive index n of the transparent dielectric layer 13) × (film thickness d of the transparent dielectric layer 13), the same effect can be obtained with a small film thickness d. It is desirable that the refractive index n of the transparent dielectric layer 13 is large.
[0064]
In FIGS. 3 and 4, the first-layer reflected light amount ratio and the second-layer reflected light ratio become maximum values when the thickness of the transparent dielectric layer 13 reaches a certain value. 13 decreases as the film thickness increases. However, since the present invention is a technology for improving light use efficiency utilizing multiple interference of light, in practice, as shown in FIG. The thickness of the layer 13 is repeatedly increased and decreased at a certain cycle, and a maximum value is generated each time the thickness of the transparent dielectric layer 13 increases by λ / 2n. FIG. 5 is a graph in which the relationship between the thickness of the transparent dielectric layer 13 and the reflectance of the first reflective layer 12 and the second reflective layer 15 is calculated by simulation, and the results are graphed.
[0065]
The graph of FIG. 5 is obtained by optical calculation using a virtual multilayer film, assuming the refractive index and the film thickness of each layer as parameters. In contrast, FIGS. 3 and 4 are normalized assuming that the reflectance is 100% when the film thickness is 0, that is, when the transparent dielectric layer is not provided, and the absolute value is different from FIG.
[0066]
The first maximum value in the first layer reflected light amount ratio and the second layer reflected light amount ratio is such that the optical path length (nd) of the transparent dielectric layer 13 is smaller than １ ／ of the wavelength of the light beam applied to the optical disk 10. It always occurs in the period when it gets smaller. That is, while the thickness d of the transparent dielectric layer 13 satisfies 0 <nd <λ / 2, the thickness of the transparent dielectric layer 13 can be set to improve the light use efficiency. However, the technical idea of the present invention is not limited to the above conditions, and the improvement of the light use efficiency using the multiple interference when the film thickness is further larger (that is, when the film thickness becomes a value at which the maximum value is obtained after the second time). Is also included.
[0067]
Further, the transparent dielectric layer 13 has a particularly remarkable effect of improving light use efficiency with respect to the first layer reflected light amount ratio rather than the second layer reflected light amount ratio. That is, since the amount of reflected light of the first reflective layer 12 is particularly enhanced as compared with the conventional example, when the second reflective layer 15 is reproduced, the reflected light of the first reflective layer 12 is added to the reflected light of the second reflective layer 15. May have an adverse effect as noise. However, as described above, when the first reflection layer 12 is used as a main recording area and the second reflection layer 15 is used as an auxiliary recording area, it is difficult to scan well with only the first reflection layer 12. Useful.
[0068]
However, in order to minimize the noise in the reflected light of the second reflective layer 15, the thickness of the transparent dielectric layer 13 should be set to a thickness that gives the maximum value of the second layer reflected light amount ratio. For example, in the case where the refractive index of the transparent dielectric layer 13 is 2.2, when comparing Example 3 with Comparative Example 1, the ratio of the first-layer reflected light amount is larger in Comparative Example 1; In the third embodiment in which the two-layer reflected light amount ratio is maximized, the difference between the first-layer reflected light amount ratio and the second-layer reflected light ratio is smaller, and the reflection of the first reflecting layer 12 with respect to the reflected light of the second reflecting layer 15. Noise due to light can be reduced.
[0069]
Further, when it is desired to maintain a balance between the amount of reflected light of the first reflective layer 12 and the amount of reflected light of the second reflective layer 15, further optimization of light use efficiency including adjustment of the film thickness of the first reflective layer 12 is possible. It becomes.
[0070]
That is, the amount of light reflected by the first reflective layer 12 can be greatly improved by multiple interference at the transparent dielectric layer 13, and the first reflective layer 12 is made thinner than 15 nm to form the first reflective layer 12. Even if the transmittance of the reflective layer 12 is increased, it is possible to obtain a larger amount of reflected light than the conventional example. On the other hand, although the amount of light reflected by the second reflective layer 15 is not improved much by the multiple interference in the transparent dielectric layer 13, the amount of light reflected by the second reflective layer 15 is distributed by reducing the film thickness of the first reflective layer 12. Can be directly improved.
[0071]
Thereby, it is possible to optimize the reflection light amount of the first reflection layer 12 and the reflection light amount of the second reflection layer 15 so as to be substantially the same. At this time, since the first reflective layer 12 only changes the transmittance and does not change the value of the refractive index due to the thinning, the multiple interference effect in the transparent dielectric layer 13 does not change. The conditions of the refractive index and the film thickness can be diverted as they are.
[0072]
If the focus of the light beam can be reliably locked to the first reflection layer 12 as described above, it is easy to move the focus of the light beam to the second reflection layer 15 based on this position. The focus can be satisfactorily locked to both 12.15.
[0073]
In addition, the thickness of the transparent dielectric layer 13 is a layer for utilizing multiple interference of light, and is on the order of several tens to several hundreds of nm. Productivity is also good because it can be formed by technology.
[0074]
Since each layer other than the transparent dielectric layer 13 has the same configuration as that of the conventional optical disk, it can be formed by a thin film technique such as spin coating or sputtering, and the productivity is good.
[0075]
In the above description, the optical disc 10 has the same structure as the substrate on which the first base material 11 is generally called, and the light is incident from the substrate side. However, in recent years, a method in which light is incident from the film surface side without passing through the substrate has been proposed for the purpose of increasing the density, and the present invention is also applicable to a reproducing method in which light is incident from the film surface side. However, in that case, the medium configuration is reversed, and therefore, as shown in FIG. 6, in the optical disc 10 ', the first base material 11, the second reflection layer 15', the second base material 14, the transparent dielectric layer 13 ', Light is incident from the protective layer 16 side in the order of the first reflective layer 12 ′ and the protective layer 16. Further, in the optical disk 10 'having the above configuration, even if the medium configuration is different, the principle of improving the light use efficiency by the optical path and the multiple interference is the same as that of the optical disk 10 described above. The present invention can be applied by changing the configuration.
[0076]
In the present embodiment, a medium having a two-layer structure has been described. However, the medium structure is not limited to two layers, and the transparent dielectric layer has a reflection / transmission function similarly to the present embodiment. By providing the layer adjacent to the reflective layer and on the side opposite to the light incident side, the present invention can be applied to a multilayer structure such as a three-layer structure or a four-layer structure.
[0077]
As described above, in the optical disc 10 according to the present embodiment, the intensity of the reflected light from the first reflective layer 12 and the second reflective layer 15 can be improved by the multiple interference effect of the transparent dielectric layer 13; According to the reproducing apparatus and the reproducing method for reproducing the optical disk 10, a favorable reproduced signal can be obtained even if the output of the irradiated light beam is reduced as compared with the conventional reproducing. For this reason, when the light beam for reproducing the optical disk 10 is set to an output suitable for this, it is possible to achieve lower power consumption than in the past.
[0078]
In addition, it is possible to reproduce the optical disk 10 even in a conventional optical disk reproducing device in which the output of the light beam is not particularly set to match the optical disk 10. In this case, the first reflective layer 12 and the By improving the intensity of the light reflected from the two-reflection layer 15, a better reproduction signal can be obtained.
[0079]
【The invention's effect】
As described above, the optical disc of the present invention includes the transparent dielectric layer disposed adjacent to the first reflective layer and providing a multiple interference effect to a light beam irradiated for information reproduction. Features.
[0080]
Therefore, when irradiating the first reflective layer with the focus of the light beam being locked, multiple reflections occur in the transparent dielectric layer, and these multiple reflections interfere with each other in a direction that enhances each other. Thus, the intensity of light reflected from the first reflective layer is improved. Also, when the irradiation is performed while the focus of the light beam is locked on the second reflective layer, multiple reflection occurs in the transparent dielectric layer when the light beam irradiated on the second reflective layer passes through the transparent dielectric layer. However, the multiple reflections of these multiple reflections cause interference with each other in a mutually reinforcing direction, so that the intensity of the reflection light from the second reflection layer is improved.
[0081]
As a result, in an optical disc having a multilayer structure having two or more reflective layers, there is an effect that the amount of light reflected from these multilayer reflective layers can be improved.
[0082]
Further, in the optical disc, it is preferable that the transparent dielectric layer is provided on a side opposite to the light incident side with respect to the first reflection layer.
[0083]
Therefore, the effect of the multiple interference in the transparent dielectric layer becomes remarkable.
[0084]
Further, in the optical disc, it is preferable that a refractive index of the transparent dielectric layer has a value larger than a refractive index of a base material which is in contact with a side opposite to the light incident side.
[0085]
Therefore, it is easy to increase the difference between the refractive index of the transparent dielectric layer and the refractive index of the base material, and the multiple interference effect can be increased. Also, there is an effect that the multiple interference effect can be obtained by reducing the thickness of the transparent dielectric layer.
[0086]
In the optical disk, the thickness of the transparent dielectric layer is defined as 0 <nd <λ / 2, where n is the refractive index of the transparent dielectric layer, d is the thickness of the transparent dielectric layer, and λ is the wavelength of the light beam. It is preferable to set within the range that satisfies.
[0087]
Therefore, by setting the thickness of the transparent dielectric layer so that the thickness of the transparent dielectric layer satisfies 0 <nd <λ / 2, the thickness of the transparent dielectric layer is minimized and the multiple interference effect is minimized. Can be obtained, and the light use efficiency can be improved.
[0088]
In the optical disc, the transparent dielectric layer is formed of AlN, SiN, AlSiN, AlTaN, TaO, SiO, SiO ₂ , TiO ₂ , ZnS, Al ₂ O ₃ , SiAlOH, MgF ₂ It is preferable to adopt a configuration consisting of any one of the above.
[0089]
Therefore, there is an effect that the transparent dielectric layer can be manufactured by applying a conventional manufacturing method.
[0090]
Further, the optical disc device of the present invention is characterized in that, as described above, the output of the light source that emits the light beam for reproducing the optical disc is set to an output suitable for reproducing the optical disc having the above configuration. I have.
[0091]
Further, the optical disk method of the present invention is characterized in that, as described above, the output of the light beam for reproducing the optical disk is emitted at an output suitable for reproducing the optical disk having the above configuration.
[0092]
In the optical disc according to the present invention, the reflected light intensity from the first reflection layer and the second reflection layer can be improved by the multiple interference effect of the transparent dielectric layer. For this reason, in the optical disk reproducing apparatus and the optical disk reproducing method for reproducing the optical disk, the output of the irradiated light beam is set to an output suitable for reproducing the optical disk as compared with the conventional reproduction, so that the conventional optical disk can be reproduced. This has the effect of achieving lower power consumption.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an optical disc having a two-layer structure showing one embodiment of the present invention.
FIG. 2 is a diagram showing a schematic configuration of an optical disk reproducing apparatus for reproducing the optical disk.
FIG. 3 is a graph showing a relationship between a film thickness of a transparent dielectric layer and a first layer reflected light amount ratio in the optical disc.
FIG. 4 is a graph showing a relationship between a film thickness of a transparent dielectric layer and a second layer reflected light amount ratio in the optical disc.
FIG. 5 is a graph showing the relationship between the thickness of a transparent dielectric layer and the reflectivity of a first reflective layer and a second reflective layer in the optical disc by a simulation result.
FIG. 6 is a sectional view of an optical disc having a two-layer structure showing another embodiment of the present invention.
FIG. 7 is a cross-sectional view of a conventional optical disc having a two-layer structure.
[Explanation of symbols]
10,10 'optical disk
12, 12 'First reflective layer
13,13 'transparent dielectric layer
14 Second base material (base material in contact with transparent dielectric layer)
15, 15 'second reflection layer
21 Laser light source (light source)

Claims (7)

An optical disc having a multilayer structure including at least one first reflection layer having a light reflection and transmission function and one second reflection layer having only a light reflection function,
An optical disc, comprising: a transparent dielectric layer disposed adjacent to the first reflection layer and providing a multiple interference effect to a light beam irradiated for information reproduction. 2. The optical disk according to claim 1, wherein the transparent dielectric layer is provided on a side opposite to the light incident side with respect to the first reflection layer. 2. The optical disk according to claim 1, wherein a refractive index of the transparent dielectric layer is larger than a refractive index of a base material which is in contact with a side opposite to the light incident side. The thickness of the transparent dielectric layer is set within a range satisfying 0 <nd <λ / 2, where n is the refractive index of the transparent dielectric layer, d is the thickness of the transparent dielectric layer, and λ is the wavelength of the light beam. The optical disk according to claim 1, wherein: The transparent dielectric layer is characterized _{AlN, SiN, AlSiN, AlTaN,} TaO, SiO, SiO 2, TiO 2, ZnS, Al 2 O 3, SiAlOH, that consist of any of the compounds of MgF ₂ The optical disc according to claim 1. An optical disc reproducing apparatus for reproducing an optical disc having a multilayer structure including at least one first reflective layer having a light reflecting and transmitting function and one second reflecting layer having only a light reflecting function,
6. An optical disc reproducing apparatus, wherein an output of a light source for emitting a light beam for reproducing an optical disc is set to an output suitable for reproducing the optical disc according to any one of claims 1 to 5. An optical disc reproducing method for reproducing an optical disc having a multilayer structure including at least one first reflective layer having a function of reflecting and transmitting light and one second reflective layer having only a function of reflecting light,
6. An optical disk reproducing method, wherein an output of a light beam for reproducing an optical disk is irradiated with an output suitable for reproducing the optical disk according to any one of claims 1 to 5.

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